UNIVERSITY    OF   CALIFORNIA 

COLLEGE    OF    AGRICULTURE 

AGRICULTURAL   EXPERIMENT  STATION 

CIRCULAR  No.  223 

November,  1920 

THE  PEAR  THRIPS1 

By  E.  O.  ESSIG 


The  pear  thrips  was  first  recorded  in  California  as  a  new  species2 
in  1904  and  for  more  than  ten  years  it  has  been  an  orchard  pest 
of  considerable  importance  in  the  counties  adjacent  to  and  in  the 
San  Francisco  Bay  region.  It  first  became  serious  in  Santa  Clara, 
Alameda,  and  Contra  Costa  counties,  but  in  later  years  developed 
importance  in  Solano,  Napa,  Sonoma,  Monterey,  San  Benito,  San 
Joaquin,  Sacramento,  Yolo,  Marin,  and  San  Mateo  counties. 

The  appearance  of  the  pear  thrips  in  the  orchards  is  sporadic; 
no  two  successive  seasons  are  alike  in  any  particular  locality.  It 
becomes  destructive  in  small  or  in  large,  widely  separated  areas  and 
may  be  very  unevenly  distributed  in  these.  It  is  seldom  that  a  large 
body  of  contiguous  orchards  is  found  uniformly  infested;  there  may 
be  a  small  district  here,  an  orchard  there,  or  a  number  of  orchards 
having  serious  outbreaks,  while  neighboring  trees  escape  injury.  It 
is  true  that  some  individual  insects  may  be  found  in  practically  all 
orchards,  but  in  many  they  are  not  found  in  sufficient  numbers  to 
injure  the  crop.  This  fact  has  not  been  entirely  explained,  but  the 
chief  factors  responsible  therefor  probably  are  climatic  conditions, 
general  orchard  practices,  artificial  control,  and  natural  enemies,  each 
of  which  will  be  considered  separately  below. 

LIFE    HISTORY 

The  pear  thrips  spends  the  larger  part  of  its  life  cycle  in  the  soil 
beneath  the  plow  sole  as  an  immature  "white  thrips"  in  aestivation 
and  hibernation.  It  enters  the  soil  in  May  and  June  and  remains 
there  until  February  and  March.  In  early  November,  a  change  in 
development  takes  place  from  the  white  larval  to  the  pupal  stage 


i  Originally  known  as  Euthrips  pyri  Daniel,  then  as  Taeniothrips  pyri  (Daniel), 
now  considered  by  European  entomologists  as  synonymous  with  Taeniothrips 
incoiisequens  Uzel,  a  widely  distributed  European  species.  The  common  name 
is  *  'thrips,"  never  "thrip, ' '  as  one  often  hears. 

2  S.  M.  Daniel,  Entomological  News,  vol.  15,  Nov.,  1904,  pp.  293-294.  Original 
description. 


Z  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

and  finally  to  the  adult  stage  of  winged  "black  thrips, "  which  emerge 
from  the  soil  with  the  first  warm  days  when  the  buds  of  the  trees 
are  beginning  to  burst.  They  continue  to  emerge  until  the  trees  are 
in  full  bloom  and  even  later.  The  adults  are  mostly  very  dark  brown 
or  almost  black  and  are  not  easily  confused  with  other  species  of 
thrips  common  in  the  orchards.  In  some  seasons  they  emerge  before 
the  buds  open  and  may  then  be  found  in  great  numbers  on  the  limbs 
and  twigs  of  the  trees.    In  the  case  of  the  prune  and  the  pear,  which 


Fig.  1. — a,  Prune  twigs,  showing  condition  of  fruit  buds  when  adult  thrips 
begin  to  attack  them.     French  prune    (left),  Imperial  prune    (right). 

B,  Portion  of  a  stem  or  petiole  of  a  prune  flower,  showing  hatching  of  young 
pear  thrips.  a,  Egg  exposed  to  view  by  removing  epidermis;  b,  young  "white 
thrips"  emerging  from  egg  under  epidermis;  c,  exit  hole  of  young  thrips;  d, 
small  nearly-hemispherical  swelling  caused  by  inserting  the  egg  under  the  thin 
epidermis.     Greatly  enlarged. 

C,  Cherry  leaf,  showing  characteristic  perforations  resulting  from  attacks  of 
young  or  "white  thrips"  when  the  leaf  was  unfolding.      (Original.) 


of  all  fruit  trees,  are  probably  the  most  seriously  injured  by  thrips, 
the  blossom  buds  open  in  small  clusters,  and  in  these  the  thrips  collect 
in  great  numbers.  After  their  long  fast,  they  are  voracious  feeders 
and  may  within  a  few  days  destroy  the  flower  buds  entirely,  even 
before  the  blossoms  begin  to  open. 

The  average  orchardist  associates  thrips  with  blossoms  and  does 
not  think  of  examining  his  trees  for  them  until  the  most  serious 
damage  is  done.  It  is  true  that  the  thrips  continue  to  emerge  from 
the  soil,  and  to  infest  and  even  seriously  injure  the  blossoms  as  well 


Circular  223  THE  pear  thrips  3 

as  the  leaf  buds  even  to  the  extent  of  making  control  measures  neces- 
sary, but  the  strategic  time  in  thrips  control  is  before  the  blossom 
buds  are  fully  open. 

Besides  feeding,  the  adults  deposit  countless  numbers  of  minute 
bean-shaped,  transparently  white  eggs  just  under  the  epidermis  of 
the  blossom  and  leaf  petioles.  The  small  distorted  areas  caused 
thereby  may  be  easily  noticed  with  the  naked  eye.  The  egg-punctures 
may  be  so  numerous  as  to  cause  a  serious  dropping  of  the  blossoms. 
In  such  cases,  however,  the  adults  are  numerous  enough  to  have 
previously  destroyed  most  of  the  buds. 

The  young  "white  thrips"  begin  to  appear  nearly  two  weeks 
after  the  blossoms  start  to  open,  at  about  the  time  the  last  blossoms 
are  opening,  or  more  often,  when  the  young  leaf  buds  are  unfolding. 
They  may  damage  the  blossoms  seriously,  but  the  chief  injury  is  to 
the  young  fruit,  still  in  the  jacket,  and  to  the  developing  leaves.  After 
two  or  three  weeks  of  feeding,  or  about  the  middle  of  May  or  first 
of  June,  the  "white  thrips"  drop  to  the  ground  and  go  into  the  soil 
to  remain  during  the  summer,  fall,  and  winter  months.  From  this 
review  it  will  be  seen  that  there  is  but  one  generation  a  year;  the 
adults  appearing  in  February,  March,  and  April  and  the  young 
"white  thrips"  leaving  in  May  and  June.  A  few  straggling  adults 
as  well  as  young  may  be  found  much  later,  especially  on  young 
nursery  trees. 

TREES    ATTACKED 

The  following  kinds  of  orchard  trees  and  vines  are  attacked :  prune, 
pear,  cherry,  plum,  almond,  peach,  apple,  fig,  English  walnut,  and 
grape,  but  only  the  four  first  named  are  seriously  injured.  Earlier 
varieties  usually  suffer  most,  but  there  are  times  when  the  later  ones 
are  greatly  injured. 

It  must  not  be  overlooked  that  other  species  of  thrips3  are  also 
commonly  found  upon  fruit  trees.  These  are  often  associated  with 
the  pear  thrips  but  may  occur  without  them. 

3  The  other  species  common  upon  deciduous  fruit  trees  are : 

The  wheat  thrips,  FranMiniella  tritioi  (Fitch),  which  is  a  rather  slender,  pale 
yellow  species  with  a  noticeable  orange-colored  prothorax.  It  may  be  associated 
with  pear  thrips  in  the  blossoms,  but  is  more  often  found  in  midsummer  and  fall, 
having  migrated  from  the  drying  grasslands,  grain,  and  alfalfa  fields.  It  is 
responsible  for  considerable  injury  to  young  peaches  in  various  parts  of  the  state. 

The  bean  thrips,  Heliothrips  fasciatus  Perg.,  is  distinguished  by  its  black  color 
and  the  dark  markings  on  the  noticeably  light-colored  wings.  It  may  be  associated 
with  the  pear  thrips  or  may  appear  later  in  the  season. 

The  greenhouse  thrips,  Heliothrips  haemorrhoidalis  Bouche,  is  a  dark  brown 
species  easily  confused  with  pear  thrips,  but  not  often  of  any  consequence. 

The  western  thrips,  Euthrips  ocoidentalis  Perg.,  is  a  small,  pale  yellow  species 
often  associated  with  pear  thrips  in  blossoms,  but  not  important  as  it  does  no 
injury. 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


CLIMATIC   CONDITIONS    INFLUENCING   THRIPS    DEVELOPMENT 

No  rules  or  regulations  based  on  climate  can  be  formulated  to 
determine  in  advance  the  abundance  or  destructiveness  of  pear  thrips 
because  little  is  known  respecting  just  how  much  this  insect  is 
influenced  by  rains  or  droughts,  and  by  cold  or  hot  weather,  but  from 
past  observations  the  extreme  of  any  of  these  over  a  period  of  several 
years  has  a  noticeably  detrimental  influence  on  development;  while 
under  what  appear  to  be  the  climatic  conditions  most  unfavorable  for 
thrips,  some  sections  are  seriously  affected.  In  commercial  fruit  grow- 
ing it  is  not  a  safe  practice  to  rely  upon  any  extreme  of  climate  to 
control  the  insect. 


GENERAL   ORCHARD    PRACTICES   AGAINST  THRIPS 

Under  general  orchard  practices  we  include  cultural  methods 
which  are  designed  primarily  for  other  purposes  than  insect  control, 
but  which  have  nevertheless  proved  to  be  of  great  value  in  checking 
the  ravages  of  pear  thrips.  Among  the  practices  are :  thorough  fall 
irrigation,  chiefly  by  flooding  from  late  September  through  October 
and  November,  deep  fall  plowing,  and  a  good  heavy  cover  crop. 


FALL  IERIGATION 

On  a  small  scale,  thorough  irrigation  by  flooding  has  been  prac- 
ticed as  a  control  measure  against  pear  thrips  in  Yolo,  Solano,  and 
Santa  Clara  counties,  and  the  results  obtained  have  been  excellent  in 
practically  all  cases.  One  farmer  who  has  followed  this  plan  in  part 
of  his  prune  orchard,  leaving  an  adjoining  part  of  the  orchard  as  a 
check,  has  for  several  years  demonstrated  conclusively  the  truth  of 
the  foregoing  statement.  Each  year  the  non-irrigated  trees  have 
suffered  heavily  from  thrips  while  those  irrigated  have  produced 
normal  crops.  In  some  sections  it  is  claimed  that  fall  irrigation  has 
not  proved  satisfactory,  but  in  most  cases  this  has  probably  been  due 
to  a  lack  of  sufficient  water  to  reach  the  young  thrips  before  transfor- 
mation to  the  adult  stage  has  taken  place.  "Winter  rains  and  spring 
irrigations  come  too  late  to  have  any  effect  since  the  adult  insects  in 
the  soil  are  more  resistant  to  unfavorable  conditions  than  the  imma- 
ture forms. 


Circular  223  THE  pear  THRIPS 


DEEP  FALL  PLOWING 


While  not  so  important  as  either  of  the  other  recommended 
practices,  this  is  the  only  one  that  can  be  employed  by  a  great  many 
farmers  who  are  unable  to  irrigate,  or  to  retain  a  cover  crop  until 
after  the  trees  bloom.  Deep  fall  plowing  disturbs  the  young  insects 
sufficiently  to  cause  a  considerable  mortality  not  obtainable  by  early 
or  late  spring  cultivation  when  the  insects  have  reached  the  adult 
stage.  It  is  a  practice  which  should  be  followed  by  orchardists  where 
the  other  methods  are  impossible. 


COVER  CEOP 

Any  kind  of  a  heavy  cover  crop  allowed  to  remain  until  the  trees 
come  into  full  bloom  has  given  excellent  results  in  thrips  control  when 
the  practice  was  followed  for  a  number  of  successive  years.  The  large 
number  of  fine  cover  crops  which  have  been  grown  in  the  Santa  Clara 
Valley  orchards  in  late  years  have  been  accompanied  by  a  decrease 
in  pear  thrips  injury.  Next  in  importance  to  growing  the  cover  crop 
is  permitting  it  to  remain  if  possible  until  the  blooming  period  is 
passed  before  plowing  under,  but  this  will  depend  upon  late  rains 
or  other  available  water  to  insure  proper  tillage.  Early  barley  has 
not  proved  so  successful  as  a  cover  crop  as  have  other  plants. 

The  cover  crop  does  not  serve  as  food  for  the  thrips,  as  many 
believe,  but  on  the  contrary  produces  a  cold,  unfavorable  soil  con- 
dition which  destroys  many  of  the  insects.  It  is  of  most  importance 
because  it  retards  their  emergence  until  after  blooming  time  when 
the  period  for  the  most  serious  damage  is  past.  During  the  spring 
of  1920  many  orchards  were  studied  with  this  factor  in  mind  and 
where  cover  crops  were  turned  under  early  the  thrips  appeared  in 
great  numbers.  Orchards  partly  plowed  early  showed  sharply  the 
difference  between  the  numbers  of  insects  present  in  plowed  and 
unplowed  parts  and  the  only  orchards  which  were  entirely  devastated 
were  those  with  no  cover  crops  at  all. 

There  are  exceptions  to  the  favorable  results  occurring  from  cover 
cropping  and  other  practices  described,  but  all  the  data  thus  far 
gathered  indicate  that  these  are  excellent  orchard  practices  for  thrips 
control. 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


CONTROL    BY    SPRAYS 

The  work  done  by  such  competent  entomologists  as  Dudley 
Moulton,  Paul  Jones,  S.  W.  Foster,  Earl  Morris,  D.  L.  Currier,  and 
others  on  the  control  of  pear  thrips  has  not  been  without  excellent 
results.  They  not  only  made  possible  the  so-called  "Government 
Formula,"   but   worked   out   the   practical   field-spraying   operations 


Fig.  2. — A  suitable  hand-duster  for  applying  nicodust  to  control  pear  thrips. 
Note  condition  of  flowers  at  time  of  making  this  particular  application.  A  high 
wind  prevented  proper  spreading  of  the  dust.     (Original.) 


which    insure    adequate    control.      The    government    formula    is    the 

following : 

Distillate  emulsion 10  gals. 

"Black  leaf  40" 1  pint 

Water   to    make 200  gals. 

When  this  formula  was  first  prepared  there  were  few  commercial  oil 
sprays  on  the  market  so  that  it  was  first  necessary  to  make  a  distillate 
emulsion.4     In  recent  years  there  have   appeared  the  miscible   oils 

Distillate  27°   Baume 20  gals. 

Fish  oil  soap 24  lbs. 

Caustic   soda   12  lbs. 

Hot  water  to  make 20  gals. 

4  Formula  for  homemade  distillate  emulsion  for  stock  use : 


Circular  223  THE  pear  THRIPS  7 

which  may  be  used  as  follows : 

Miscible  oil  5  gals. 

"Black  leaf  40" 1  pint 

Water   to   make 200  gals. 

These  formulae  are  for  use  against  the  adult  "black  thrips"  and 
should  be  applied  liberally  as  soon  as  any  considerable  number  of 
insects  is  found  upon  the  trees.  Do  not  fail  to  make  daily  inspections 
after  buds  begin  to  swell!  Applications  should  be  repeated  if  neces- 
sary until  the  adults  begin  to  lessen  in  numbers. 

In  case  the  "white  thrips"  appear  in  destructive  numbers  later, 
the  same  formula  may  be  safely  used  if  the  oil  content  is  decreased 
and  the  nicotine  increased  as  follows: 

Distillate  emulsion  6  gals. 

"Black  leaf  40" iy2  pints 

Water   to   make 200  gals. 

Miscible  oil   3  gals. 

"Black  leaf  40" 1%  pints 

Water   to   make 200  gals. 

For  work  with  thrips,  the  greater  force  and  volume  delivery  of 
the  spray  gun  has  rendered  it  superior  to  the  spray  rod,  insuring  not 
only  a  better,  but  a  quicker  and  easier  job.  The  loss  in  material 
occasioned  thereby  is  more  than  overcome  by  the  rapidity  and  ease 
of  operation. 

CONTROL  BY  DUST  SPRAYS 

The  development  of  the  nicotine  dust  sprays  for  aphis  control 
suggested  the  use  of  dusts  in  combating  thrips.  Dust  sprays  offer 
advantages  over  liquids  in  cost,  saving  of  time,  and  ease  of  applica- 
tion. The  power  equipment  necessary  is  not  expensive,  and  suitable 
hand-dusters  may  be  had  at  a  very  low  cost.  A  power-duster  with 
one  operator  and  a  driver  can  cover  from  20  to  30  acres  a  day,  while 
one  man  with  a  hand  machine  can  dust  only  from  3  to  5  acres  a 
day.  These  are  important  factors  in  thrips  control  where  only  limited 
time  is  allowed.  Where  rainy  weather  conditions  are  likely  to  make 
it  impossible  for  a  power  sprayer  to  be  moved  over  the  soft  ground, 
a  light  power-blower  or  hand-blower  can  be  used  effectively.  The 
owner  of  a  small  orchard  can  well  afford  to  have  at  least  one  hand- 
blower  to  care  for  his  own  trees. 

With  these  factors  in  mind  a  large  number  of  tests  were  made 
with  5  per  cent  "Nieodust,"  containing  5  per  cent  "Black  leaf  40" 


8 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


or  2  per  cent  of  pure  nicotine.  The  dust  used  for  carrying  the 
nicotine  is  finely  pulverized  kaolin,  an  inert  clay.  A  power-blower 
and  hand-dusters  were  used  and  widely  separated  orchards  treated. 
Experiments  were  also  made  next  to  sprayed  trees. 

The  results  of  the  work  demonstrated  clearly  that  the  5  per  cent 
"Nicodust"  readily  killed  all  exposed  thrips.  It  was  more  efficient 
against  the  adult  "black  thrips"  than  against  the  "white  thrips" 


Fig.    3. — Applying   nicodust   with    a   power-dusting   machine   to    control   pear 
thrips.    A  good  distribution  of  the  dust  is  being  accomplished.     (Original.) 


hidden  in  the  tightly  curled  unfolding  leaves.  After  dusting,  the 
thrips  usually  drop  from  the  twigs  immediately  so  that  but  few  dead 
individuals  can  be  found  on  the  trees. 

The  most  efficient  killing  occurs  during  the  heat  of  the  day  because 
of  the  rapid  volatilization  of  the  nicotine,  so  that  an  early  start  in 
the  morning  when  the  temperature  is  low  may  prove  to  be  a  waste 
of  time  and  material. 

It  required  about  *4  pound  of  "Nicodust"  per  average  sized  tree 
and,  at  a  cost  of  fifteen  cents  per  pound,  this  would  amount  to  three 
and  three-fourths  cents  per  tree  for  material.  The  cost  of  application 
may  be  estimated  by  a  calculation  based  upon  an  average  treatment 


Circular  223  THE  PEAR  thrips  9 

of  20  acres  per  day  with  a  power  machine  and  two  men  and  three 
acres  per  day  with  a  hand  machine  and  one  man. 

Dusting  for  adult  " black  thrips"  gave  practically  as  good  results 
as  spraying.  Dusting  for  "white  thrips"  was  effective,  killing  all 
exposed  insects,  but  was  not  quite  so  effective  as  a  single  spraying, 
owing  to  the  greater  penetrating  power  of  the  oil  sprays,  but  two 
dustings  can  be  made  at  almost  the  same  cost  as  one  spraying, 
and  if  properly  timed  would  give  much  better  results  than  a  single 
spraying.5 


NATURAL   ENEMIES 

The  natural  enemies  of  the  adult  pear  thrips  are  few.  The  young 
thrips  in  the  soil  appear  to  be  practically  free  from  parasites  and 
predators,  but  those  on  the  trees  are  preyed  upon  by  the  insidious 
plant  bug,  Triphleps  tristicolor  White,  the  larvae  of  the  California 
green  lacewing,  Chrysopa  oalifornica  Coq.,  those  of  the  brown  lace- 
wing,  Hemerobius  oalifomicus  Banks  and  H.  pacificus  Banks,  the 
larvae  of  the  common  ladybird  beetle,  Hippodamia  converges,  syrphid 
fly  larvae,  etc.,  but  as  yet  natural  enemies  appear  to  be  an  unimportant 
factor  in  the  control  of  thrips. 


5  This  work  will  be  continued  by  the  writer  during  the  coming  season,  working 
under  the  State  Deciduous  Fruits  appropriation  through  the  University  of  Cali- 
fornia Deciduous  Fruit  Experiment  Station,  at  Mountain  View,  in  cooperation 
with  County  Horticultural  Commissioner  L.  E.  Cody,  Deputy  Horticultural  Com- 
missioner D.  L.  Currier,  and  Professor  W.  L.  Howard,  all  of  whom  have  aided 
very  greatly  in  securing  the  information  contained  in  this  article. 


STATION  PUBLICATIONS  AVAILABLE  FOR  FREE  DISTRIBUTION 


BULLETINS 


No. 
185. 

251. 

253. 

257. 
261. 
262. 

263. 
266. 

267. 
268. 
270. 


271. 
272. 
273. 

274. 

275. 

276. 

278. 
279. 
280. 

282. 

283. 
285. 
286. 


No. 

Report  of  Progress  in  Cereal  Investiga-  288. 

tions. 

Utilization  of  the  Nitrogen  and  Organic  290. 

Matter    in    Septic    and    Imhoff    Tank 

Sludges.  298. 

Irrigation    and    Soil    Conditions    in    the  299. 

Sierra  Nevada  Foothills,  California.  300. 

New  Dosage  Tables.  301. 
Melaxuma  of  the  Walnut,  "  Juglans  regia." 

Citrus    Diseases    of    Florida    and    Cuba  302. 

Compared  with  Those  of  California. 

Size  Grades  for  Ripe  Olives.  303. 

A  Spotting  of  Citrus  Fruits  Due  to  the  304. 

Action  of  Oil  Liberated  from  the  Rind. 
Experiments  with  Stocks  for  Citrus.  308.  I 
Growing  and  Grafting  Olive  Seedlings. 
A  Comparison  of  Annual  Cropping,  Bi- 
ennial  Cropping,   and   Green   Manures  309.  I 

on  the  Yield  of  Wheat. 

Feeding  Dairy  Calves  in  California.  310. 

Commercial  Fertilizers.  311. 

Preliminary    Report    on    Kearney    Vine-  312. 

yard  Experimental  Drain.  313. 

The  Common  Honey  Bee  as  an  Agent  in  316. 

Prune  Polination.  317. 

The  Cultivation  of  Belladonna  in   Cali-  318. 

fornia.  319. 

The  Pomegranate.  320. 

Grain  Sorghums.  321. 

Irrigation  of  Rice  in  California.  322. 

Irrigation   of  Alfalfa  in  the  Sacramento  323. 

Valley. 

Trials   with   California   Silage   Crops   for  324. 

Dairy  Cows. 

The  Olive  Insects  of  California.  325. 
The  Milch  Goat  in  California. 
Commercial  Fertilizers. 


Potash  from  Tule  and  the  Fertilizer 
Value  of  Certain  Marsh  Plants. 

The  June  Drop  of  Washington  Navel 
Oranges. 

Seedless  Raisin  Grapes. 

The  Use  of  Lumber  on  California  Farms. 

Commercial  Fertilizers. 

California  State  Dairy  Cow  Competition, 
1916-18. 

Control  of  Ground  Squirrels  by  the 
Fumigation  Method. 

Grape  Syrup. 

A  Study  on  the  Effects  of  Freezes  on 
Citrus  in  California. 
Fumigation  with  Liquid  Hydrocianic 
Acid.  II.  Physical  and  Chemical  Pro- 
perties of  Liquid  Hydrocianic  Acid. 
The  Carob  in  California.  II.  Nutri- 
tive Value  of  the  Carob  Bean. 

Plum  Pollination. 

Investigations  with  Milking  Machines. 

Mariout  Barley. 

Pruning  Young  Deciduous  Fruit  Trees. 

The  Kaki  or  Oriental  Persimmon. 

Selections  of  Stocks  in  Citrus  Propagation. 

The  Effects  of  Alkali  on  Citrus  Trees. 

Caprifigs  and  Caprification. 

Control  of  the  Coyote  in  California. 

Commercial  Production  of  Grape  Syrup. 

The  Evaporation  of  Grapes. 

Heavy  vs.  Light  Grain  Feeding  for  Dairy 
Cows. 

Storage  of  Perishable  Fruit  at  Freezing 
Temperatures. 

Rice  Irrigation  Measurements  and  Ex- 
periments in  Sacramento  Valley,  1914- 
1919. 


CIRCULARS 


No. 

70.  Observations    on    the    Status     of    Corn 

Growing  in  California. 
76.  Hot  Room  Callusing. 
82.  The      Common      Ground      Squirrels      of 

California. 

113.  Correspondence  Courses  in  Agriculture. 

114.  Increasing  the  Duty  of  Water. 

115.  Grafting  Vinif era  Vineyards. 

117.  The  Selection  and  Cost  of  a  Small  Pump- 
ing Plant. 
124.  Alfalfa  Silage  for  Fattening  Steers. 

126.  Spraying  for  the  Grape  Leaf  Hopper. 

127.  House  Fumigation. 

128.  Insecticide  Formulas. 

129.  The  Control  of  Citrus  Insects. 

130.  Cabbage  Growing  in  California. 

131.  Spraying  for  Control  of  Walnut  Aphis. 

135.  Official  Tests  of  Dairy  Cows. 

136.  Melilotus  Indica. 

137.  Wood  Decay  in  Orchard  Trees. 

138.  The  Sdo  in  California  Agriculture. 

139.  The  Generation  of  Hydrocyanic  Acid  Gas 

in  Fumigation  by  Portable  Machines. 

140.  The   Practical   Application    of    Improved 

Methods  of  Fermentation  in  California 
Wineries  during  1913  and  1914. 

143.  Control     of     Grasshoppers     in     Imperial 

Valley. 

144.  Oidium  or  Powdery  Mildew  of  the  Vine. 
148.  "Lungworms". 

152.  Some  Observations  on  the  Bulk  Handling 

of  Grain  in  California. 

153.  Announcement    of    the    California    State 

Dairy  Cow  Competition,  1916-18. 

154.  Irrigation    Practice    in    Growing    Small 

Fruits  in  California. 

155.  Bovine  Tuberculosis. 


No. 
156. 
157. 
158. 
159. 
160. 
164. 
165. 

167. 
168. 


170. 

172. 
173. 
174. 
175. 

176. 

177. 
178. 
179. 

181. 
182. 

183. 
184. 
185. 

187. 
188. 
189. 
190. 
191. 


How  to  Operate  an  Incubator. 
Control  of  the  Pear  Scab. 
Home  and  Farm  Canning. 
Agriculture  in  the  Imperial  Valley. 
Lettuce  Growing  in  California. 
Small  Fruit  Culture  in  California. 
Fundamentals    of    Sugar    Beet    Culture 

under  California  Conditions. 
Feeding  Stuffs  of  Minor  Importance. 
Spraying  for  the  Control  of  Wild  Morning- 

Glory  within  the  Fog  Belt. 
The  1918  Grain  Crop. 
Fertilizing  California  Soils  for  the   1918 

Crop. 
Wheat  Culture. 

The  Construction  of  the  Wood-Hoop  Silo. 
Farm  Drainage  Methods. 
Progress  Report  on  the   Marketing  and 

Distribution  of  Milk. 
Hog  Cholera  Prevention  and  the  Serum 

Treatment. 
Grain  Sorghums. 

The  Packing  of  Apples  in  California. 
Factors  of  Importance  in  Producing  Milk 

of  Low  Bacterial  Count. 
Control  of  the  California  Ground  Squirrel. 
Extending  the  Area  of  Irrigated  Wheat  in 

California  for  1918. 
Infectious  Abortion  in  Cows. 
A  Flock  of  Sheep  on  the  Farm. 
Beekeeping  for  the  Fruit-grower  and  Small 

Rancher  or  Amateur. 
Utilizing  the  Sorghums. 
Lambing  Sheds. 
Winter  Forage  Crops. 
Agriculture  Clubs  in  California. 
Pruning  the  Seedless  Grapes. 


CI  RC  UL  ARS— Continued 


No. 

193.  A  Study  of  Farm  Labor  in  California. 
198.  Syrup  from  Sweet  Sorghum. 

201.  Helpful  Hints  to  Hog  Raisers. 

202.  County     Organization     for     Rural     Fire 

Control. 

203.  Peat  as  a  Manure  Substitute. 

204.  Handbook    of   Plant    Diseases   and    Pest 

Control. 

205.  Blackleg. 

206.  Jack  Cheese. 

207.  Neufchatel  Cheese. 

208.  Summary  of  the  Annual  Reports  of  the 

Farm  Advisors  of  California. 
210.  Suggestions  to  the  Settler  in  California. 

213.  Evaporators  for  Prune  Drying. 

214.  Seed    Treatment   for   the    Prevention    of 

Cereal  Smuts. 


No. 
215.  Feeding  Dairy  Cows  in  California. 

217.  Methods    for    Marketing    Vegetables    in 

California. 

218.  Advanced  Registry  Testing  of  Dairy  Cows. 

219.  The  Present  Status  of  Alkali. 

220.  Unfermented  Fruit  Juices. 

221.  How  California  is  Helping    People  Own 

Farms  and  Rural  Homes. 

222.  Fundamental  Principles  of  Co-operation 

in  Agriculture. 

223.  The  Pear  Thrips. 

224.  Control  of  the  Brown  Apricot  Scale  and 

the  Italian  Pear  Scale  on  Deciduous 
Fruit  Trees. 

225.  Propagation  of  Vines. 

226.  Protection    of    Vineyards    from    Phyl- 

loxera. 


